Adjusting device of an apparatus for generating a beam of charged particles

ABSTRACT

This device comprises adjustment means ( 40 ) for storing the desired characteristics for the beam ( 14 ), determining the values of the adjustment parameters of the apparatus ( 2 ) according to its characteristics, storing these values and giving these stored values to the adjustment parameters of the apparatus. The invention is applied in particular to the manufacturing of nanostructures.

TECHNICAL FIELD

The present invention relates to an adjusting device of an apparatus for generating a beam of charged particles.

The invention particularly relates to an adjusting device of an apparatus for generating an ion beam and more particularly to an adjusting device of an instrument for nanomanufacturing with an ion beam.

One tries to adjust in particular the size of an ionic probe i.e. the size of the focused ion beam which is sent onto a target, as well as the shape of the ion distribution in this ionic probe at the target are attempted.

The invention is in particular applied to the manufacture of structures with very small sizes, less than 50 nm, and more particularly to the manufacture of nanostructures with sizes of the order of 10 nm or less.

The invention finds applications in various fields such as electronics (in particular with regard to devices—for example single electron transistors), ultra high density data storage (using nanostructures formed on magnetic materials) and ultra high speed semiconductor devices (using nanostructures formed on semiconducting materials).

The present invention is in particular applied to adjusting an ion beam emitted by an apparatus comprising an ion point source, i.e., an ion source with a very bright emissive point area.

Further, this ion point source is preferably an LMIS, i.e., a liquid metal ion source.

STATE OF THE PRIOR ART

Concerning liquid metal ion sources, one may refer to the following documents:

[1] International application PCT/FR 95/00903, International publication NO. WO 96/02065, invention of Jacques Gierak and Gérard Ben Assayag, corresponding to patent US-A-5,936,251.

[2] US-A-4,426,582, invention of J. H. Orloff and L. W. Swanson.

In addition, apparatuses generating ion beams called FIB and producing focused ion beams are known. But it should be noted that with these FIBs, it is not possible to manufacture good quality nanostructures with sizes less than 50 nm.

Further, a device for adjusting the shape of a focused ion beam is known from the following document:

[3] US-A-4,704,726, invention of H. Kyogoku and T. Kaito (Seiko Instruments and Electronics Ltd.).

The adjusting technique disclosed in this document [3] is only a transposition of the adjusting technique conventionally used in scanning electron microscopy or ion beam lithography.

Such a technique cannot be used in the nanometric range.

Further, this known technique requires the preliminary manufacturing of costly and fragile calibration markers which are not reusable.

In addition, according to a known technique, for adjusting an apparatus generating an ion beam, it is the operator himself/herself who checks the various operating parameters of the ion optical system of the apparatus and who should make sure that the results of the adjustments give a theoretical resolution which is consistent with the intended use for the ion beam.

This step is delicate as it is subject to interpretation and compromise.

The operator is sometimes provided with tabulated data to facilitate his/her task, for example, the values of the ionic optical system's resolution versus the ionic probe current values for various distances between this ionic optical system (comprising a set of electrostatic lenses) and the target of the ion beam.

However, adjusting the apparatus remains delicate.

DISCLOSURE OF THE INVENTION

The object of the present invention is to find a remedy to the above drawbacks.

The invention in particular is directed to adding self-adjustment, self-diagnose and self-calibration capacity to an apparatus for generating an ion beam.

By adding such capacities to the apparatus, it is possible to improve and to widen the field of applications of this apparatus as well as the productivity of the latter, by almost totally excluding the intervention of an operator, i.e. a user of the apparatus.

More generally, the present invention proposes an adjusting device of an apparatus for generating a charge particle beam, with which the intervention of an operator is almost totally excluded.

Specifically, the object of the present invention, is an adjusting device of an apparatus for generating a beam of charge particles, in particular an ion or electron beam, wherein this beam is for interacting with a target, this device being-characterized in that it comprises adjusting means for:

storing the desired characteristics for the particle beam, as determined by the user of the apparatus,

determining the values of the adjustment parameters of the apparatus according to these characteristics and storing these values, and

giving these stored values to the adjustment parameters of the apparatus.

According to a particular embodiment of the invention, the adjustment means are additionally for:

continually or periodically measuring these parameters, when the beam of charged particles interacts with a target and determining the characteristics of the beam from these measurements:

comparing the thereby determined characteristics with the stored characteristics, and

if at least one of the thereby determined characteristics lies outside a predefined amplitude range, centered on the corresponding stored characteristic, changing the adjustment parameters of the apparatus and/or informing the user of the apparatus.

According to a preferred embodiment of the invention, the charged particles are ions, the target is a substrate, the apparatus comprises an ion source, means for accelerating these ions and means for focusing these ions, this apparatus is for manufacturing a structure, in particular a nanostructure, on the substrate, the ion beam is capable of eroding this substrate, and the adjustment means are for:

storing the desired characteristics for the ion beam, as determined by the user of the apparatus according to the structure to be manufactured,

determining the values of the adjustment parameters of the apparatus according to these characteristics and storing these values, and

giving these stored values to the adjustment parameters of the apparatus.

Preferably, the adjustment means are further for:

continually or periodically measuring these parameters, during the manufacturing of the structure, and determining the characteristics of the beam from these measurements,

comparing the thereby determined characteristics to the stored characteristics, and

if at least one of the thereby determined characteristics lies outside a predefined amplitude interval, centered on the corresponding stored characteristic, changing the adjustment parameters of the apparatus and/or informing the user of the apparatus.

The characteristics of the ion beam may comprise the size and the current density of this ion beam.

Preferably, the adjustment means are further for applying the following steps:

controlling the apparatus in order to form on the substrate, in an area of this substrate which is not intended for the formation of the structure, a test imprint according to a stored reference digital imprint,

digitizing the test imprint,

comparing the digitized test imprint with the stored reference digital imprint, and

if these imprints are different, changing at least one of the adjustment parameters of the apparatus, and repeating these steps until a suitable adjustment of the apparatus is obtained.

According to a particular first embodiment of the invention, the adjustment means are further for:

measuring the adjustment parameters of the apparatus at any time or periodically during the manufacturing of the structure, and

if at least one of the parameters drifts and therefore leaves-a predefined amplitude range, centered on the corresponding stored parameter, changing the measured parameter so that it is again found in this range.

According to a particular second embodiment, the adjustment means are further for:

measuring the adjustment parameters of the apparatus at any time or periodically during the manufacturing of the structure, and

in the event of any instability of at least one of these parameters, interrupting the manufacturing process and informing the user and/or calibrating the apparatus for adjusting this parameter again.

In this case, the adjustment means are preferably provided for applying the following steps in order to calibrate the apparatus:

controlling this apparatus so as to form on the substrate, in an area of this substrate which is not intended for the formation of the structure, a test imprint according to a stored reference digital imprint,

digitizing the test imprint,

comparing the digitized test imprint with the stored reference digital imprint,

if these imprints are different, changing the adjustment parameter of the apparatus and repeating these steps until a suitable adjustment of the apparatus is obtained.

The adjustment parameters may comprise the emission current of the ion source, the energy of the ions, the focusing of the ion beam, the amplitude of the writing field on the substrate, the correction of stigmatism and the distance between the apparatus and the substrate.

SHORT DESCRIPTION OF THE DRAWINGS

The present invention will be better understood upon reading the description of exemplary embodiments given hereafter, purely as an indication, and absolutely not as a limitation, by referring to the single appended FIGURE which is a schematic view of a particular embodiment of the device of the invention.

DETAILED DISCUSSION OF PARTICULAR EMBODIMENTS

In this FIGURE; an example of an apparatus 2 for generating an ion beam to which the invention may be applied, is illustrated schematically.

This apparatus 2 comprises an ion source 4 for example with a liquid metal, which is for producing an ion beam, for example, formed with gallium ions, a system 6 for extracting and accelerating the produced ion beam, a source support 8 and an electrostatic optical system 10.

The axis of the system 10 is marked as Z1 and the axis of the ion beam 12 emitted by the source 4 as Z, axes Z and Z1 being parallel.

The assembly formed by the source 4, its support 8 nd the system lQ forms the focused ion column of the apparatus 2. System 10 essentially consists of electrostatic lenses (not illustrated) for focusing the beam 12 in order to form a focused ion beam 14.

In order to align the central axis Z of the emission cone of the ion beam 12 (axis of the source 4) with the optical axis Z1 of the electrostatic optical system 10, the source support is provided with a set 16 of micrometric stages. This set 16 symbolized by dot and dash lines in the FIGURE allows the support 8 to be displaced along an X axis and a Y axis which are perpendicular to each other as well as.to the Z axis.

The FIGURE also shows a substrate 18 to be treated by the focused beam 14 and forming a target for this beam (which is capable of eroding this substrate 18).

This substrate is mounted on a stage 20 which may be displaced along three axes respectively perpendicular to axes X, Y and Z.

The apparatus 2 is for manufacturing a nanostructure on the substrate 18.

Additionally, a control system 22 or an operating system of the device 2 for generating an ion beam is seen.

This system 22 comprises:

means 24 for controlling the ion source 4,

means 26 for controlling the system 6 for extracting and accelerating the ion beam 12,

means 28 for controlling the. electrostatic optical system 10, and

means 29 for controlling the assembly 16 of micrometric stages.

Means 30 for controlling the displacement of the substrate bearing stage 20 are also seen.

A technique is considered in the following which is directed to solving the basic problem of the adjustment of the parameters of an ion column providing an ionic probe at the scale of tens of nanometers, in order to form nanometric size structures by controlled ion irradiation.

The geometrical shape (size), the profile (a more or less sharp decrease in the number of particles when moving away from the central axis of the beam) dominate, as well as the sphericity of the distribution in the ionic probe at the target. At a scale of a few nanometers, the problems are all the more complicated.

This technique is directed to providing a very accurate and fast adjustment of the profile of this ionic probe. The relevant points are:

focusing (concentration) of the ion beam 12 under the action of the electrostatic lenses of the apparatus 2, at the target formed by the substrate 18, into a spot (impact) with nanometric dimensions,

correcting the lack of sphericity of the incident ionic probe, and

calibrating the writing field (a field which may be addressed by the beam under the action of electrostatic deflectors which the electrostatic optical system 10 comprises) at the surface of the target, so that the relative position is always accurately known within a few nanometers.

Use of a ion beam focused into a 10 nm spot for nanomanufacturing applications has specific. constraints:

the sputtering effect induced by energetic ions which bombard the target, sooner or later leads to the destruction of the calibration structures (generally gold markers on silicon) which are conventionally used in electron beamn lithography, for example).

Moreover, calibrated structures of a few tens of nanometers are delicate to manufacture, very brittle and expensive above all.

The period of use of the ion beam may attain several hours, which imposes periodic checks on the characteristics of this ion beam in order to limit the influence of drifts and transient instabilities.

The reduced working distances which are required for obtaining a geometrical magnification of the source spot less than 1, all the more reduce the usable depth of field.

Moreover, certain substrates include patterns with heights which highly differ from one another, so that these patterns are not all located at the ideal focal distance.

In the latter case, a ion which falls on such a substrate at the optical axis (Z1 axis) covers a much shorter path than another ion which has been deflected from this axis by several millimeters.

This optical path difference causes the occurrence of defects or aberrations.

In order to limit these aberrations to an acceptable value, the writing size is limited in a field of the order of a hundred micrometers.

Thus, without any appended device, the FIB nanomanufacturing technique can only form small elementary patterns.

When an ultra accurate displacement of substrate 18 is used, the possibility of linking up several elementary substructures occurs for defining a large size pattern. But this remains dependent on strict calibration of the size of the FIB elementary writing field.

Indeed, a most complete match as possible between the coordinates of the points defined within a scanning field and the displacement coordinates of the substrate bearing stage 20 is required.

All this is complex because the scanning of the ionic probe is obtained by means of a CAD (computer-aided design) generator of the digital/analog type (contained in the control means 28) whereas the stage 20, as far as it is concerned, is driven by control means 30 formed by a specific and independent interface 30.

It should also be noted that any variation in the distance between the substrate and the ionic column, in the energy of the ions or the nature of the latter, changes the value of the amplitude of the scanning field.

The considered technique is fast, highly accurate, and capable of being automated for calibrating the optical system 10 of the ionic column, by utilizing the property that heavy incident ions such as gallium ions or ions of other metals e.g. aluminium ions, have, of locally etching the target which they strike.

With this technique, a same apparatus for generating an ion beam is capable of forming its own calibration marks and then of checking them fully autonomously.

The considered technique utilizes the eroding effect of the incident ion beam generated by the apparatus 2 for generating ion beams, for etching a simple structure, according to a predetermined CAD pattern, for example of the square, single hole (“spot”) or cross type, in a “sacrified area”.

After etching the substrate by FIB, this structure is then imaged by the apparatus 2 which is then operated in the SIM (Scanning Ion Microscopy) mode, under the same conditions, without any change, by simply collecting via suitable detection means 32, the secondary electrons 34 which result from the scanning of the surface of the substrate 18 by the ion-beam 14.

Electronic processing means 36 equipped with display means 38 are provided for processing the signals provided by these detection means 32.

The SIM image obtained via the detection means is digitized by the electronic processing means 36 and on this digitized SIM image corresponding to the actually etched structure, it is then possible to superimpose by computer the digitized initial predetermined pattern (square, hole or cross for example) and to (digitally) differentiate both images.

In the case of a square type pattern for example, a defect originating from poor focusing may then be detected and a remedy may be found by increasing stepwise the focusing effect of the lenses of the beam generating apparatus 2. The process may be automated for various magnifications and repeated step-by-step, until the digitized SIM image and the initial pattern fully coincide.

It is also possible to take advantage of the same eroding effect for correcting a possible lack of sphericity, also called an astigmatic defect, at the spot of the incident ions. In this case, a perfect image of the imprint of the ionic probe may be obtained very rapidly, in a few tenths of a second, by boring a single hole of the order of 10 to 20 nm.

If an elliptical profile of the spot is revealed, always by comparing with an ideal reference image (circular image), and according to the orientation of the obtained ellipse, it is possible to trigger a corrective and iterative test procedure, until the decision criterion established by the users is met and the computer system used then exits this sequence (preferably automatically).

The calibration of the size of the FIB writing field is the last crucial point which may be applied preferably automatically, with the considered technique. First, lines are etched (a network of parallel lines or a network of crossed lines) with a length known with very little uncertainty.

To do this, the ion beam is maintained in the spot mode and does not scan the surface of the substrate 18 whereas the latter is moved via the stage 20 which supports this substrate, the measurement of the displacements of this stage being conducted by laser interferometry. Mechanical precision may then fall down to a few nanometers (of the order of 10 nm to 5 nm).

In this case, the markers are not formed by scanning the surface of the target 18 with the ionic probe 14, but only formed by displacing this target, the central Z1 axis of the etching ion beam being kept fixed.

An SIM image of the thereby manufactured structures then enables after digitization of this image, the gain of the amplifier stage of the beam generating apparatus 2 to be adjusted so that a digital weight of one or a few bits corresponds to a known displacement (of a certain number of nanometers) at the substrate 18.

Calibration of the scanning field is then performed with a laser interferometry measurement technique.

According to the present invention, a device is proposed, which is complementary to the technique considered above, and adds to its significance.

The proposed device notably tends to improve and make the adjustment more effective of the parameters of a unique ionic column delivering an ionic probe at the scale of tens of nanometers, in order to form nanometric sized structures by controlled ion irradiation.

In particular, different levels of assistance are proposed to the user of an apparatus for generating a beam of charged particles and more particularly a beam of ions:

Determination of the optimal parameters for utilizing the apparatus according to the required operating conditions, i.e.:

-   -   selection of an optical mode for obtaining the required         resolution (for example, the energizing voltage of the focusing         lenses, working distance, semidivergent mode, semiconvergent         mode or collimated mode (in the optical system) or the need for         a “cross over” i.e. a crossing of charged particles, in         particular, ions in the optical system),     -   size of the writing field, detection of distortion effects and         quantification of these effects,

and then, in connection with the computer program of the pattern scanning generator (contained in the operating system 22 of apparatus 2), validation of these parameters or further detection of the impossibilities or conflicts between parameters (for example, the precision level of the scanning or of the incident ion dose).

Determination of the parameterization of the ionic probe provided by the optical system:

-   -   characteristic of the current distribution (for example, width         or standard deviation)     -   value of the transported current checking the adjustments of the         apparatus:

By utilizing the property which heavy incident ions (gallium ions or other metal ions) have, of locally etching the target which they strike, the beam generating apparatus may produce its own calibration marks and then image them in scanning ion microscopy.

With this, the consistence of these markers may then be checked against the result which is elaborated beforehand in a device according to the invention, formed by an adjustment module, a computation module, which is integrated into the operating system 22 of the apparatus 2.

An example of a device according to the invention is provided hereafter.

It is assumed that the intention is to accomplish a certain sequence of nanomanufacturing with apparatus 2.

According to the invention, the system 22 is completed by an adjustment module 40 or computation module.

This module 40, essentially including a computer, provides information to the operator (the user of the apparatus) via the display means 38. The operator, as far as he/she is concerned, is lead to provide information (notably data) to module 40, information which is symbolized by the arrow 42 in the FIGURE.

Furthermore, for implementing the invention, the adjustment module 40 is connected to various control means 24, 26, 28, 29 and 30, which the operating system 22 of the apparatus 2 includes, in order to control these means 24, 26, 29 and 30.

The latter are equipped with suitable sensors (not shown) which allow them to know the state of various units 4, 6, 10, 16 and 20, which they control.

In addition, module 40 is connected to detection means 32 and electronic processing means 36 in order to control the operation of the apparatus in the scanning ion microscopy mode and to exploit the results from this operation.

According to the invention, adjustments are proposed to the operator, these adjustments being determined by the computation module. Then the operator starts the nanomanufacturing sequence.

Module 40 then continually (or periodically but then with a high rate) computes the properties of the ionic probe (ion beam 14) during this nanomanufacturing sequence and compares the computational result to pre-established values, stored in this module 40.

If the values obtained during the calculation are different from these pre-established values, the module undertakes corrective measures by adjusting the parameters for adjusting the apparatus or, if the difference between the results of a calculation and the pre-established values is too large, module 40 informs the operator via the display means 38.

More specificallyi according to the invention, the adjustment module 40 stores the desired characteristics for the ion beam 14, as determined beforehand by the user of the apparatus 2 according to the structure to be manufactured on the substrate 18.

Next, module 40 determines the values of the adjustment parameters of apparatus 2 according to these characteristics and stores these values.

And then the module gives these values which it has stored, to the adjustment parameters of the apparatus 2 via the control means 24, 26, 28 and 30, to which module 40 sends control signals enabling the desired adjustments to be made.

The characteristics of the ion beam 14 are the size of this ion beam and the current density in this beam.

The adjustment parameters of the ion column, as for them, are the following:

the emission current of the ion source 4,

the energy of the ions,

the voltages applied to the focusing lenses,

the amplitude of the scanning field, i.e., the amplitude of the writing field,

the correction of stigmatism of the ion beam 14,

the distance between the apparatus and the target 18, this distance being adjusted by displacing the stage 20 parallel with the Z1 axis.

It should be noted that when the operator wants to make a too large correction of stigmatism, the computation module 40 informs this operator about this via the display means 38.

Moreover, during the manufacturing of the structure on the substrate 18, module 40 may measure these parameters either continually or periodically (preferably with a high rate) and determine the characteristics of the beam 14 from these measurements (which are made via means 24, 26, 28 and 30).

The module then compares the thereby determined characteristics with the stored characteristics. When one or more of these thereby determined characteristics differ (by a predefined percentage, for example ranging from −10% to +10%) from the characteristic or the corresponding stored characteristics, the module informs the operator and again changes the adjustment parameters of the apparatus to obtain the proper characteristics for beam 14.

If the differences are too large, module 40 may simply inform the operator and wait for instructions from the latter for proceeding with the manufacturing.

In addition, before starting the manufacturing of this structure and during the latter, module 40 may apply the following steps:

-   -   This module controls apparatus 2 in order to form on the         substrate 18, in an area of this substrate which is not intended         for forming the structure, a test imprint according to a         reference digital imprint stored beforehand in module 40.     -   The module then compares the digitized test imprint with the         stored reference digital imprint.     -   If these imprints are different, the module changes one or more         of the adjustment parameters of the apparatus 2 and repeats the         relevant steps until it obtains a proper adjustment of this         apparatus.

Further, module 40 may be programmed so as to act on the apparatus (via control means 24, 26 and 28 in the event of any drift of one or more parameters). Indeed, it should be noted that a manufacturing sequence generally lasts a long time, for example 2 hours.

As module 40 is able to (continually or periodically) measure the parameters, it may detect the drift of the latter and remedy it.

Moreover, module 40 may be programmed so that it interrupts the manufacturing sequence (and informs the operator about it) in the event of an instability of one or more parameters, i.e., in the event of a sudden change of the latter.

In this case, it may be anticipated that the module 40 starts a phase for calibrating the apparatus 2, according to a technique mentioned earlier, which uses the formation of patterns (for example crosses or holes) in an area of the substrate 18 where the structure is not formed.

It should be noted that the calibration is made without requiring the intervention of the operator. The module itself controls the creation of the required etchings in the substrate 18, in order to adjust the parameter(s) again, module 40 changing the latter until a proper adjustment is obtained.

Further, it should be noted that the nanomanufacturing process takes place at a very low pressure; for one reason or another, this pressure may increase very rapidly; also, a problem of an electrical nature is liable to affect the apparatus 2; in such cases, the module 40 cannot act by itself and requires intervention of the operator.

The present invention is not limited to the adjustment of an apparatus for generating a (positive or negative) ion beam. It also applies to the adjustment of other apparatuses for generating beams of charged particles such as electron microscopes, the particles then being electrons. 

1. An adjustment device of an apparatus (2) for generating a beam of charged particles (14), in particular an ion or electron beam, wherein this beam is for interacting with a target (18), this device being characterized in that it comprises adjustment means (40) provided for: storing desired characteristics for the beam of particles, as determined by the user of the apparatus, determining the values of the adjustment parameters of the apparatus according to these characteristics, and storing these values, and giving these stored values to the adjustment parameters of the apparatus. 